Room temperature-curable resin compositions are generally classified into two categories, namely, one-part moisture curable-compositions (one-part compositions) and two-part moisture curable compositions (two-part compositions). In the case of a one-part moisture curable composition, the prepolymer and the cross linking agent which are necessary for curing are stored in the same container, and the composition starts curing upon exposure to moisture. On the other hand, in the case of a two-part room temperature-curable composition, the prepolymer which constitutes the main part and the curing agent are stored in separate containers, and the curing starts when these two parts are mixed. Since the main part and the curing agent which are necessary for the curing are stored separately from each other in a two-part composition, the composition enjoys excellent long term storage stability and use of a highly reactive compound for the curing agent is allowed. In addition, since the two parts, namely, the main part and the curing agent are mixed immediately before use, the resin composition enjoys both the surface curability and the depth curability which are better than those of the one-part composition. While the one-part composition has advantage in the handling convenience since the components required for the curing are stored in one container in the ready-to-use state, its storage stability is clearly inferior to the two-part composition. In addition, the one-part composition is inferior in the surface curability and depth curability compared to the two-part composition since use of a highly active cross linking agent (curing agent) is prohibited.
The two-part curable composition comprises the main part and the curing agent. However, the type of the curing agent that can be used in a particular curable composition is limited by the type of the prepolymer used for the main part. For example, when a urethane prepolymer is used for the main part, the curing agent selected is often a polyol compound or an aromatic amine compound which has a relatively low reactivity since use of an aliphatic amine curing agent having a highly reactive active hydrogen results in the rapid reaction of the curing agent with the isocyanate group of the urethane prepolymer, and exothermic reaction, geleation, and the like are likely to take place in a period as short as several seconds making the required stirring difficult to be carried out.
When an epoxy resin is used for the main part, the curing agent used may be selected from a wide variety of curing agents including the highly reactive aliphatic amine curing agent and thiol group-containing curing agent since epoxy group is not so reactive at room temperature. Use of an aliphatic amine curing agent having a high curability is then a practical choice and use of other curing agent is not very popular.
However, use of an amine curing agent is impractical not only when the urethane prepolymer is the only prepolymer of the main component but also when both the urethane prepolymer and the epoxy resin are used for the prepolymers due to the abrupt reaction of the amine curing agent with the urethane prepolymer. While such problem may be solved by the use of an amine latent curing agent (for example, see JP 2002-235067 A [the term “JP XX-XXXXXX A” as used herein means an “unexamined published Japanese patent application”]), a latent curing agent presents active hydrogen only after its hydrolysis which proceed at a quite low speed detracting from the excellent depth curability unique to the two-part resin composition. Another way of overcoming such challenge is use of an amine adduct which had been formed by reacting an epoxy resin with an excessive amount of polyamine for the curing agent of various prepolymers. An amine adduct, however, is a highly viscous substance due to its high molecular weight, and it suffers from extremely poor mixing workability. In addition, blend ratio of the amine adduct with the prepolymer is not alterable since an amine adduct should be blended at a proportion equivalent to the isocyanate group of the urethane prepolymer. Accordingly, use of an amine adduct had the drawback of the unchangeable blend ratio between the urethane prepolymer and the epoxy resin (for example, see Hiroshi KAKIUCHI, “New Epoxy Resin [first edition]”, Japan, Shoko-do Publishing Company, Sep. 20, 1986, p.183–185). In view of the situation as described above, a strong demand exists for a curing agent or a curing component which can be used with a urethane or other prepolymer that has a highly reactive functional group, and which can be used with any two or more prepolymers.